As is known in the art, one technique used to inject high-speed differential signals into, or sense such high speed differential signals in, printed circuit boards (PCBs) is to use a differential signal probe such as shown in FIGS. 1A and 1B. Here, a probe 9 has a pair of semi rigid coax cables 10a, 10b, each have an outer ground shield or housing 12 around a central, inner signal conductor or pin 14, each such pin 14 being dielectrically insulated from the other pin 14 and from the outer ground shield 12. The distal end of the probe 9 has a plug/receptacle 16 to which an SMA cable, not shown, can be connected. The signal pins 14 are adapted to connect to a differential signal launch 20 comprising a pair of vertically extending electrically conductive signal vias 22a, 22b having contacts on the upper surface of a printed circuit board (PCB) 26. The signal vias 22a, 22b are electrically connected to a corresponding one of a pair of horizontally extending signal conductors 24a, 24b, respectively, disposed within the PCB 26. The pair of signal conductor 24a, 24b are disposed between a pair of horizontally extending ground plane conductors 28a, 28b, as shown in FIG. 1B. Here, the arrangement is a floating ground arrangement. An arrangement using a reference ground is shown in FIGS. 2A and 2B where a piece of wire 30 is attached at one end to the outer ground conductor of the probe 9 and at the other end to a ground via 32 which passes through the PCB 26 to the ground plane conductors 28a, 28b. The use of a wire creates a large return route thereby degrading your signal.
In another arrangement, a Surface Mount Adapter (SMA) receptacle on the printed circuit board, as shown in FIGS. 5A and 5B. The Surface Mount Adapter is used with the outer shield of the housing grounded to a pad on the printed circuit board. This pad also acts as an anchor point for the component. However, this pad is a fixed distance, depending on the location of the ground leg of the SMA. Because the SMA can be in different configurations, the ground pads are made to suite the anchor points. Further, another disadvantage of this arrangement results from the size of the SMA's footprint. Typically, a 0.975 in×0.975 in area is needed for a differential pair. This limits the amount of signals one can probe on a test board. A differential trace would have to be split to be routed to the center pin thereby causing impedance discontinuities. Further, because of the physical height and size of the connector, there are limitations on where it could be placed and what applications it could be used.